1. Field of the Invention
The present invention relates to mirror-embedded light transmission media and fabrication methods thereof, which offer excellent characteristics in terms of cost, mass production and reliability.
2. Description of Related Art
With the recent development of information and communication technology typified by the Internet as well as a recent dramatic increase in processor speeds, there has been a growing demand for the transmission of high volume data such as image and motion video. In such high volume data transmissions, there is a demand for transmission rates of 10 Gbps or more as well as a small effect of electromagnetic noise. Among such high-speed communications, optical transmissions, which are not affected by electromagnetic noise, have shown great promise. In this context, conventionally employed electrical transmissions using metal cables and wiring are being replaced by optical transmissions using optical fibers and waveguides.
Mainly in order to reduce the mounting costs in such optical transmission systems, there has been proposed an optical waveguide that mounts therein a photonic device (such as a surface light emitting device and a surface light receiving device) in parallel to its core. In this technology, the optical path needs to be deflected approximately 90° in order to optically couple the core and the photonic device. A means for realizing this is to form a V-groove in the core by cutting or dicing and to fabricate a mirror on an angled surface of the V-groove. For example, such a mirror is provided by reflection at the bare angled surface formed in the waveguide and, in this case, its reflectivity is determined from the refractive index difference between the air and the waveguide (core) material. Another method of forming such a mirror is to form a metal film on the above-mentioned bare angled surface by vapor depositing a metal such as gold (for these methods e.g., see JP-A Hei 10 (1998)-300961).
In the above methods, an optical fiber may be used instead of a waveguide. In this case, similarly, a V-groove is formed, by dicing or the like, in an optical fiber mounted on a substrate. Then, a mirror is formed in the core of the optical fiber by utilizing an oblique surface of the V-groove. Hereinafter, an optical waveguide and an optical fiber are collectively referred to as a light transmission medium.
However, the mirror utilizing the bare surface cut by means of, e.g., a dicing blade has a surface roughness (many projections and depressions), and therefore has a problem of increased light reflection loss (mirror loss) due to degraded reflection efficiency. In particular, when a soft material is cut like that, the resulting cut surface tends to be comparatively rougher. Hence, when a flexible optical waveguide or a flexible optical fiber is processed by dicing, the resulting diced surface is remarkably rough.
On the other hand, the mirror provided by the metal-deposited surface has problems with cost because the number of waveguides loadable in a vapor deposition chamber becomes limited with increasing size of the waveguide. Furthermore, a vapor-deposited metal film generally has poor adhesiveness to an optical waveguide material, thus posing a problem of peeling.